Recent research has documented the central role of panic attacks in the development of agoraphobia and a frequent occurrence of psychiatric and medical comorbidity in patients with Panic Disorder. Specifically, it appears that in addition to commonly developing agoraphobia, many Panic Disorder patients manifest social phobia, major depression, alcoholism, suicidality, and cardiovascular morbidity. Such research has, however, primarily targeted younger patients, and studies of this disorder in the elderly are virtually non-existent. Further, little knowledge exists of the characteristics of this disorder when it presents for the first time in old age. Our preliminary studies indicate that patients with late- onset Panic Disorder (LOPD) (onset at age 55 and above) present with a phenomenologically distinct picture compared to patients with early-onset Panic Disorder (EOPD). the present study aims to establish and extend these findings in a large sample of Panic Disorder patients. We propose to investigate a total of 150 subjects with Panic Disorder divided equally in three groups as follows: 1) 50 Subjects, age 55 and above, onset of Panic Disorder at or after age 55 (LOPD group); 2) 50 Subjects, age 55 and above, onset of Panic Disorder before age 55 (older EOPD group); 3) 50 Subjects with age range of 18-54 (younger EOPD group). The LOPD group will be compared to both EOPD groups. Two comparison groups will permit us to examine the significance of age of onset as well as of chronological age. The central tent of this study is that the syndrome of LOPD is different phenomenologically from EOPD, with possibly different vulnerability factors and comorbidity. We hypothesize that: 1) LOPD subjects will differ phenomenologically from EOPD subjects in manifesting fewer symptoms during panic attacks, having fewer fearful cognitions, reporting less avoidance behavior, and manifesting less somatization; 2) compared to older EOPD subjects, LOPD subjects will manifest less comorbidity and thus report less frequent lifetime history of social phobia, depression, alcoholism, suicide attempts, and cardiovascular morbidity; 3) LOPD subjects will report less frequent family histories of Panic Disorder and more frequent identifiable stressors related to onset of Panic Disorder compared to EOPD subjects. This study will provide an in-depth characterization of LOPD and will clarify whether it is a qualitatively distinct syndrome. It will also contribute clinically important information regarding course of illness of and comorbidity associated with long-standing Panic Disorder in older EOPD subjects. This will provide foundation and direction for more definitive treatment and prevention research, and public health planning for this potentially debilitating illness in older adults.